I'd suggest a standard AR, mil spec stuff. 16 inch, 1 in 7 barrel. Nothing fancy, put good optics on it, (ACOG) keep the handguard short and light, keep it light overall, and enjoy it for what it is, a lighweight, compact, high capacity, easy to wield, capable little rifle.
I clearly understand the pull of a specialized, high end gun. with a 2 foot long, keymod handguard, forward grip, BUIS, match barrel and so on. However, the AR platform and 223 being what it is, I see no need to make it as heavy as a 308 with all sorts of additional stuff. In fact, I strongly dislike unbalanced, nose heavy AR's
I see no real world benefit from piston uppers either. Nor do I see a reliability improvement by going with a piston upper. Both gas impingement and piston uppers are equally reliable.
Piston uppers may have a downside as the piston driven AR "may" be less accurate. And parts are uncommon. Suppressors are said to be better paired with a gas gun, not a piston, for tuning.
I have tens of thousands of rounds downrange. The only AR reliability issues I've ever had are related to the ammo and not the gun. I don't throw my guns down the gravel driveway, and I don't pour sand into a fine piece of machinery. I keep my stuff clean and properly maintained. Surprisingly, that works every time.
If you want to shoot longer distances, go for a 308.